Viral vectors have a long track record in therapeutic gene delivery and intervention. Current efforts are starting to bear fruit, as more viral vector therapies are reaching the later stages of clinical development. Since the discovery of adeno-associated virus (AAV), a variety of serotypes and variants have been described and characterized, with AAV2 being the most widely studied. The single-stranded DNA (ssDNA) genome, which is flanked by two inverted terminal repeats (ITRs), can be replaced by any gene (maximum z5kb) to create a rAAV vector genome. AAV vector technology has advantages that make it one of the most attractive solutions for therapeutic gene delivery. It is possible to transduce both dividing and nondividing cells with AAV vectors, and long-term transgene expression can be achieved in post-mitotic cells. Besides, AAV exhibits low immunogenicity, and no adverse events have been reported during past clinical trials.

AAV vectors are currently among the most commonly applied for in vivo gene therapy methods. The evaluation of vectors during clinical development requires the production of considerable amounts of highly pure and potent vectors. The scale of production is mainly determined by the number of virus particles required per batch. For adenovirus production, a scale associated with the cultivation of up to 10¹⁵ virus particles (VP)/batch or less may be normally produced in up to 100 L bioreactor for gene therapy applications. A process that allows the robust and reproducible manufacturing of a drug at the required scale, with the required yields and purity, is important for its clinical development and commercial viability.